This invention relates generally to the field of turbines or power plants that produce electricity from fluid flow, either air or water, and more particularly relates to such devices wherein the fluid flow causes rotation of a propeller-type rotor, with the rotation being transferred to generators to produce the electricity.
Production of electricity using hydroelectric or wind-powered turbines is well known. The fluid flow causes rotation of a propeller-type rotor or blades. For wind-powered turbines, the devices are located in areas with steady air currents, and the devices are typically rotated so as to be oriented in the optimum direction for capturing the wind energy. For hydroelectric turbines, the devices are placed in fast moving water currents, typically as part of a dam structure. Such water flow conditions are known as high head conditions.
While most turbines are constructed to have a central rotating shaft onto which the blades or runners are mounted, it has been found that open-centered turbine constructions can have benefits not found with turbines having centralized shafts. Turbines having open-centered rotors, where the blades are mounted between inner and outer annular rings or rims and where the energy is transferred through the outer rim, can be successful in low head conditions, i.e., in slower currents. This is due to several reasons, including the fact that elimination of the central shaft and centralized blade portions reduces drag and the fact that larger diameter rotors can be produced since weight is reduced, thereby increasing the surface area contacting the low head flow. Another benefit to open-centered turbines in hydroelectric applications is that since water flow through the central portion of the turbine is not obstructed by blades, fish are able to pass through.
Examples of such open center turbines can be seen in my U.S. Pat. No. 5,592,816 issued Jan. 14, 1997, and reissued as RE38,336 on Dec. 2, 2003, U.S. Pat. No. 6,648,589 issued Nov. 18, 2003, U.S. Pat. No. 6,729,840 issued May 4, 2004, and U.S. Patent Appl. Publication US2005/0031442 published Feb. 10, 2005.
Because the fluid flow in these turbines is unidirectional, the force applied against the blades and rotors is also uni-directional. Thus, to date it has only been necessary to address frictional issues on the down-stream or down-wind side of the rotor where the outer rim is retained by the housing, since the flow will exert pressure in only one direction. In open-centered turbines it is the trailing edge of the outer rim that must be supported by the housing, while the leading edge of the outer rim is not subjected to down-stream or down-wind pressure.
It is an object of this invention to provide a hydroelectric turbine or power plant that is operational in bi-directional water flow without requiring physical reversal of the turbine, where bi-directional flow comprises flow in one direction over a certain time period and reversed flow in the opposite direction over a subsequent time period. It is a further object to provide such a turbine and its method of use in opposing bidirectional low head water flow conditions. It is a further object to provide such a turbine capable of producing electricity in bidirectional tidal flow applications and the method of extracting electrical power from tidal flow.